Plant Sex

Food security is defined as everyone having access to sufficient, safe, and nutritious food. This has been a concern for decades, and advances have been made toward reaching this goal. In the 1960s, the ‘Green Revolution’ saw grain production double in some countries thanks to new cultivars. Notably, this included dwarf wheat varieties developed by Norman Borlaug, who has been credited with saving one billion lives.

Once again, in 2015, we face an impending food crisis. Earth’s population has been booming at an unprecedented rate. In 2011, the Day of 7 billion was declared, and by 2050 we expect the Day of 10 billion. This will place a huge strain on agriculture. To have sufficient food, agricultural output needs to increase by approximately 60%. Currently, this output only increases at an average of 1.1% per year. And just to make it worse, climate change will bring a wave of issues all of its own!

So why are we struggling?

GMOs (genetically modified organisms) that can be produced within two years are still not permitted for human consumption in the EU, and so we are still largely reliant on traditional breeding methods. Developing crops this way can take decades. Why? It turns out that plants are not particularly good at recombining their genes; this is why we are interested in plant sex!

Specifically, we’re interested in meiosis: the production of gametes, during which inter-homolog recombination occurs, and genetic diversity is introduced. This shuffling of alleles is what the traditional breeding methods rely on. Yet our main food crops maize, rice, wheat, and barley have biological constraints on where these sites of recombination (crossovers) occur. In barley, for example, only the ends of the chromosomes recombine, leaving the gene-rich interstitial and proximal regions relatively untouched. This limits the genetic variation available to breeders.

We need to learn how to manipulate meiosis; we need to find key players in the recombination process, and work out if changing their role can allow us to harness all of the allelic variation available. The chromosome axis is a key area of current research, as it is proposed that where the axis bends when placed under torsional strain is what designates a crossover site. This is because crossovers cut straight through the chromosome axis in preparation for swapping that section of the chromosome with its homolog, therefore reducing tension in that area.

The questions we ask therefore relate to how we might be able to increase tension along the axis to induce the requirement for more crossovers. Related to this is the question of crossover interference: the phenomenon identified in 1914 that crossovers tend to form far away from each other due to ‘interference’. Can we manipulate how far the interference ‘signal’ spreads, allowing crossovers to form more closely together?

Agriculture is finally paying the price for years of selecting for homogeneity, and what we now require are tools to influence what genes we can introduce into new cultivars.